Ductility of Structural Steel Members Governed by Fracture

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1. Experimental Simulation of Fracture in Large-Scale TestingFracture test was done by using cold-formed square steel tubes. It was found that the fracture process is composed of crack initiation, crack penetration, and final fracture. The mechanical properties represented by uniform elongation and Charpy impact value have a significant influence on the fracture.2. Crack Initiation StrainFrom fracture testing, in which material strength, welding condition, notch shape, size, and loading program are changed, it was found that the crack initiation strain is governed by the uniform strain pertinent to the material. Furthermore, the fact is useful for practice that the crack initiation strain is not affected by size.3. Seismic Performance of Structures Having Brittle ColumnsDynamic response analysis of steel frames having brittle columns showed that such frames have the risk of dynamic progressive failure. In order to avoid the failure, the frame should be assigned more strength than ordinary ductile frames, and the strength amplification factor is proposed.4. Design GuideDesign guide to avoid brittle fracture in steel structures during a big earthquake is established on the basis that the fracture is conservatively predicted by the crack initiation.